1. Field of the Invention
The present invention generally relates to semiconductor devices and, more particularly, to a semiconductor device having a three-dimensional structure in which a plurality of semiconductor devices and semiconductor elements are stacked, and a manufacturing method of such a semiconductor device.
With the development of electric equipments in recent years, a demand for miniaturization in dimensions and thickness, multi-function, high-performance and high-density in the semiconductor devices has been increasing. In order to cope with such a demand, the structure of the semiconductor devices has been shifting to a three-dimensional structure in which a plurality of semiconductor devices or a plurality of semiconductor elements are stacked.
2. Description of the Related Art
Japanese Laid-Open Patent Application No. 2001-223297 discloses an example of a semiconductor device, which has a three-dimensional structure formed by stacking a plurality of semiconductor devices. FIG. 1 is a cross-sectional view of the semiconductor device disclosed in the above-mentioned patent document.
In FIG. 1, semiconductor chips 3 are mounted on both sides of each of interposers 1, and are encapsulated by a seal resin 2, respectively. The two interposers 1 are stacked with the seal resin 2, which encapsulates the semiconductor chip 3, interposed therebetween. The interposers 1 are connected to each other by bonding solder balls 7 to ball pads 5 which are exposed in through holes 6 formed in a solder resist 4. That is, the upper and lower interposers 1 are electrically connected to each other by the solder balls 7, and are also connect mechanically to each other.
In the semiconductor device shown in FIG. 1, since each semiconductor chip mounted on the stacked interposers is encapsulated by the seal resin, it is necessary to provide a distance between two interposers, which distance is greater than the thickness of the seal resin layer interposed between two interposers. Therefore, if the distance between the interposers can be reduced, the overall height of the semiconductor device can also be reduced.
Additionally, since the interposers are connected and fixed to each other by the solder balls provided in the peripheral portion of the interposers, if a warp occurs in the interposers in a stacking process of an assembling process of the semiconductor package, a defect may occur in the connecting part between the interposers. Moreover, when mounting the complete semiconductor package onto a substrate, a defect may occur in the connecting part between the interposers due to a thermal deformation of the interposers and remelting of the solder balls.
Furthermore, since the complete semiconductor package is mechanically connected by a small area with only the solder balls, a stress tends to be concentrated into the connecting part between the interposers, which may deteriorate mechanical reliability of the package.